RPM GSE, L-Arginine, Caffeine, Naringin, Theobromine, and Cocoa- works great for endurance work, and has been around forever:J Strength Cond Res. 2010 May;24(5):1306-12.Effects of arginine-based supplements on the physical working capacity at the fatigue threshold.

The purpose of the present study was to examine the effects of daily oral administration of arginine-based supplements for 4 weeks on the physical working capacity at the fatigue threshold (PWCFT). The PWCFT test is an electromyographic (EMG) procedure for estimating the highest power output that can be maintained without neuromuscular evidence of fatigue. The study used a double-blind, placebo-controlled design. Fifty college-aged men (mean age +/- SD = 23.9 +/- 3.0) were randomized into 1 of 3 groups: (a) placebo (n = 19); (b) 1.5 g arginine (n = 14); or (c) 3.0 g arginine (n = 17). The placebo was microcrystalline cellulose. The 1.5-g arginine group ingested 1.5 g of arginine and 300 mg of grape seed extract, whereas the 3.0 g arginine group ingested 3.0 g of arginine and 300 mg of grape seed extract. All subjects performed an incremental test to exhaustion on a cycle ergometer to determine their PWCFT before supplementation (PRE) and after 4 weeks of supplementation (POST). Surface EMG signals were recorded from the vastus lateralis using a bipolar electrode arrangement during the incremental tests for the determination of the PRE and POST supplementation PWCFT values. There were significant mean increases (PRE to POST) in PWCFT for the 1.5 g (22.4%) and 3.0 g (18.8%) supplement groups, but no change for the placebo group (-1.6%). These findings supported the use of arginine-based supplements, at the dosages examined in the present investigation, as an ergogenic aid for untrained individuals.

If we are talking pure endurance and non stim. I would say beta alanine and Drive. The cordyceps really increase my endurance in a way other endurance based products haven't before. Plus the added test boosting and thyroid stimulation really helps with leaning out.